Logamatic R2107 blowing internal fuse

BPR2107

Logamatic R2107 blew the internal 0.4A fuse. Installed a new one, the R2107 came on, I set the time, showed boiler temp, hot water and outside temp. Everything working fine, yet 15min later it blew the fuse again. In manual mode the burner fires and works. Thoughts?

STEVEusaPA

Well it's obviously either an internal short or something else is shorting out somewhere else in the system. Time to be a detective.
I'd use a Short-Pro Tool or equivalent in place of the fuse, and turn it back on and start your troubleshooting.
Manual mode makes me think something more related to low voltage wiring.

BPR2107

Thanks. Since the sensors: hot water, outside temp, boiler temp where shown on the display, was thinking it is not a short in these.

GW

Sensors are ohm readings, not able to blow fuses. I vote it’s a line voltage issue. Did a pump kick on and blow the fuse? Popper Fuse is my go to in these situations 

pecmsg

BPR2107 said:

Thanks. Since the sensors: hot water, outside temp, boiler temp was thinking it is not a short in these.

You really need someone on site to troubleshoot. 

TAG

GW said:

Sensors are ohm readings, not able to blow fuses. I vote it’s a line voltage issue. Did a pump kick on and blow the fuse? Popper Fuse is my go to in these situations 

That's a good idea ..... do you just replace -- or just for testing?

BPR2107

Does anyone know the correct resistance across the low voltage connects 1 and 2 for blue FA (outdoor sensor). Mine is 35.27K ohms without any wires connected (so no sensor connected). I tried Buderus technical support and they were not able to provide an answer.

BPR2107

Following up. Turns out the problem was the wire going to the outdoor temperature sensor. The wire was run from the Logamatic R2107, out the back of the boiler, up the supply pipe and then outdoors. This is where it gets interesting. The wire was zipped tied to the supply pipe, and had been for 15 years. What had happened over time was the heat from the supply line had deteriorated the wire such that when the temperate got hot enough in the boiler it would short. Would work fine as long as the boiler temperate was lower, but on really cold days, the Logamtic would raise the boiler temperate and if things were just right (or wrong), the wire would short; on the coldest days, when heat was needed the most! Fix was to replace the wire and route it away from heat sources. Finding this took considerable investigation, as everything would be fine, no shorts or conductivity issues for most of the time. Hope this helps someone else if they ever have a similar problem.